The relationship of calcium movements to smooth muscle excitation will be studied in vascular and nonvascular tissue. In intestinal smooth muscle the relationship between calcium entry and muscarinic agonist activity will be examined. This will give information on the relationship between Ca entry and contraction. The activities of a new series of Ca 2 ion antagonists based on the 4-aryl-1,4-dihydropyridine structure will be examined in this tissue and an attempt made to formulate a quantitative SAR and to correlate their activities with x-ray structure. A further investigation of the mode of action of the ionophore A 23187 will be made. In several vascular and nonvascular tissues from normotensive and spontaneously hypertensive rats determinations will be made of any relationship between Ca 2 ion content, kinetics, Ca 2 ion antagonist action and changes in vascular reactivity associated with the hypertensive state.